1. Field of the Invention
The present invention relates to a structure and a manufacturing method of an electrostatic speaker. More particularly, the present invention relates to a structure and a manufacturing method of a spacer in a flat plane electrostatic speaker.
2. Description of Related Art
The most direct two senses of human being are visual and auditory systems, so for quite a long time, scientists are devoting to develop related element or system techniques. Recently, electroacoustic speakers are mainly classified into a direct radiating type and an indirect radiating type, and are approximately classified into dynamic speakers, piezoelectric speakers, and electrostatic speakers according to driving manners. Recently, the dynamic speaker is most widely used, and has a mature technology, so it is the main technology dominating the whole market. However, due to the disadvantages of the original architecture, the volume cannot be flattened, and therefore, the dynamic speaker cannot meet the requirement of the trend that the 3C (computer, communication, and consumer electronics) products become increasingly smaller and the family theater becomes flatter. As for a piezoelectric speaker, piezoelectricity of a piezoelectric material is utilized, such that when an electric field is applied on the piezoelectric material, the material deforms, so as to push a vibrating film to sound. Although the structure of the speaker is flattened and microminiaturized, it cannot be flexible as the piezoelectric material requires to be sintered.
Recently, the market of the electrostatic speaker is mainly hi-end earphones and loudspeakers. The operating principle of the conventional electrostatic speaker is sandwiching a conductive vibrating film with two fixed electrode plates with openings to form a capacitance, supplying direct voltage bias to the vibrating film and giving audio alternating voltage to the two fixed electrodes, thereby driving the conductive vibrating film to vibrate by a electrostatic force generated by positive and negative electric fields, so as to radiate the audio out. The bias of the conventional electrostatic speaker must be up to hundreds to thousands of volts, so it is necessary to externally connect amplifiers with high unit price and large volume, and it is the reason why it cannot be popularized. The structural design of using the electrostatic speaker together with the ferroelectric vibrating film may reduce the audio driving voltage, however, the electrostatic effect of the vibrating film makes the electrode contact with the vibrating film and the speaker fail to sound.
In technical application related to flexible electronics, sound is an important factor. However, the flexible electronics must have characteristics of soft, thin, having low driving voltage, and flexible, so it is a key point how to adopt the flat plane electrostatic speaker, together with the selection of the flexible material, to break through the conventional fixed speaker design structure, and to finish sound components with the features required by the flexible electronics.
For the electrostatic speaker, an electroacoustic transducer is provided in US patent publication NO. 3,894,199. As shown in FIG. 1, a holding member 11 made of an insulating material holds two fixed electrodes 120. A vibrating film 130 is located between the two electrodes. The fixed electrode 120 has many holes 121 for the radiation of the sound to pass through. A polarization voltage 141 flows through the vibrating film 130, each fixed electrode 120, and passes through a step-up transformer 140 and a resistor 142. A primary winding of the step-up transformer 140 is connected to a signal source 15. Potentials of the two fixed electrodes 120 are provided by an alternating signal of the signal source 15. The potentials of the two fixed electrodes are opposite, that is, one is positive and the other is negative.
In view of the above, the holding member 11 is only used to hold the fixed electrodes 120, and no spacer exists between the vibrating film 130 and the fixed electrodes 120. It can be known that recently related design description on the spacer of the flat plane speaker has not been proposed yet.